There are many instances of station-to-station communication systems employing optical signals transmitted between the stations via one or more waveguides, a typical case being a remotely controlled vehicle which is guided from a stationary control station. In such a system, control signals are transmitted from the control station to the vehicle and signals produced by sensors in the remote vehicle, e.g. by a television camera or other sensor means, are transmitted from the vehicle to the control station. Another example is a point-to-point intercommunication system in which two users communicate directly with each other.
In communication systems of this kind, it is important that the operator should have built-in means for testing at least one of the communicating stations, e.g. the control station in case of a system for the remote control of a moving vehicle, in order to determine whether or not that station is functioning properly.
Known communication systems of the kind specified do not have a built-in testing means and it is therefore the object of the present invention to provide for the first time communication systems of the kind specified with built-in testing means in at least one of the stations.